I had visit manali in Feb and it is really one of the best destination of Himachal. But at that time Rohtang Pass was closed due to heavily snow fall and i missed it.
There are various activities which you can do such as Ice-Skiing, River Rafting, Visiting Hidimba Devi Temple, Mata Vaishno Devi Temple, Kullu Shawl Industry, Gurudwara, Parwati Spring Water and Mall Road.